U.S. patent number 4,640,747 [Application Number 06/790,389] was granted by the patent office on 1987-02-03 for process for surface treatment of copper product.
This patent grant is currently assigned to Mitsui Mining and Smelting Co., Ltd.. Invention is credited to Naotomi Takahashi, Kuniki Ueno.
United States Patent |
4,640,747 |
Ueno , et al. |
February 3, 1987 |
Process for surface treatment of copper product
Abstract
A process for surface-treating copper products, for example, a
copper foil to be used for a copper-clad laminate, the resulting
surface-treated copper product having a superior bond strength to a
base material, resistant to etching solution, acids, etc., is
provided, which process comprises electrically depositing a binary
alloy consisting of 95 to 20% by weight of zinc and 5 to 80% by
weight of nickel, on the surface of a copper product to form a
coating layer, followed by laminating the resulting copper product
onto a base material under heating and pressure, said binary alloy
being converted during the lamination into a ternary alloy of zinc,
nickel and copper constituting a boundary layer having a superior
bond strength between the copper product and the base material.
Inventors: |
Ueno; Kuniki (Saitama,
JP), Takahashi; Naotomi (Saitama, JP) |
Assignee: |
Mitsui Mining and Smelting Co.,
Ltd. (JP)
|
Family
ID: |
16957172 |
Appl.
No.: |
06/790,389 |
Filed: |
October 23, 1985 |
Foreign Application Priority Data
|
|
|
|
|
Nov 6, 1984 [JP] |
|
|
59-233572 |
|
Current U.S.
Class: |
156/151; 29/840;
205/111; 205/246; 205/255 |
Current CPC
Class: |
C25D
5/10 (20130101); C25D 5/605 (20200801); H05K
3/384 (20130101); C25D 5/50 (20130101); C25D
3/562 (20130101); C25D 3/565 (20130101); C25D
5/627 (20200801); Y10T 29/49144 (20150115); H05K
2203/0307 (20130101); H05K 2203/1105 (20130101); H05K
2201/0355 (20130101); H05K 2203/0723 (20130101) |
Current International
Class: |
C25D
3/56 (20060101); C25D 5/48 (20060101); C25D
5/50 (20060101); C25D 5/10 (20060101); H05K
3/38 (20060101); C25D 005/50 () |
Field of
Search: |
;204/37.1,35.1,44.2,43.1,40,44,20 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Demers; Arthur P.
Attorney, Agent or Firm: Jeffers, Irish & Hoffman
Claims
What is claimed is:
1. A process for surface-treating a copper product, which process
comprises electrically depositing a binary alloy consisting of 95
to 20% by weight of zinc and 5 to 80% by weight of nickel, on the
surface of a copper product to form a coating layer, followed by
laminating or heat-pressing copper product thus obtained onto a
base material so as to convert said binary alloy into a ternary
alloy of zinc, nickel and copper.
2. A process for surface-treating a copper product according to
claim 1 wherein said surface of a copper product is a roughened
surface formed by a granular copper layer electrically deposited on
the copper product.
3. A process for surface-treating a copper product according to
claim 2 wherein said copper product is a copper foil to be used for
a copper-clad laminate.
4. A process for surface-treating a copper product according to
claim 3 wherein said coating layer has a thickness of 0.001 to 0.15
.mu.m.
5. A process for surface-treating a copper product according to
claim 3 wherein said coating layer has a thickness of 0.001 to 0.01
.mu.m.
6. A process for surface-treating a copper product according to
claim 3 wherein said binary alloy consists of 90 to 50% by weight
of zinc and 10 to 50% by weight of nickel.
7. A process for surface-treating a copper foil according to claim
1 wherein said electro-deposition of a binary alloy is carried out
using an electrolyte containing as fundamental components,
potassium pyrophosphate, zinc pyrophosphate and nickel
pyrophosphate.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for surface-treating copper
products, for example, a copper foil used for printed circuits or
the like. More particularly it relates to a process for
surface-treating a copper foil by making ternary alloy of
zinc-nickel-copper on the surface of the foil, which prevents
reduction of peel strength between copper foil and base material
caused by corrosion with an etching solution or an aqueous solution
of hydrochloric acid, etc.
2. Related Art Statement
Copper-clad laminates have usually been used for printed circuits
and prepared by bonding a copper foil a base material. The surface
of the copper foil with which the base material is bonded has been
subjected to various chemical or electrochemical treatments.
Namely, in order to enhance the bond strength of the foil onto the
base material, a granular copper layer has been electrically
deposited on the surface of the copper foil to form a roughened
surface, followed by coating the roughened surface of the
electrically deposited copper with a metal such as zinc, tin,
nickel or brass (U.S. Pat. No. 3,585,010, U.S. Pat. No. 3,377,259,
U.S. Pat. No. 2,802,897).
This zinc layer prevents the granular copper from migration, and
also prevents spotting or staining after etching the copper foil.
The layer has a thickness to such an extent at the high bond
strength of the granular copper layer is not reduced.
During lamination said copper foil is usually heat pressed. By
application of heat and pressure, zinc layer is converted into
brass by mutual diffusion between the zinc layer and copper
substrate and exhibits yellow color. Thus after laminating the
copper foil with base material, the resulting boundary forms a
brass layer.
When a printed circuit is produced using said copper-clad laminate,
the following processes are employed: The copper-clad laminate is
punched or drilled. The inside of the holes are activated, and
copper is uniformly deposited thereon by means of non-electrolytic
plating, followed by electrolytic plating to increase the copper
thickness. Then photoresist is applied onto said copper foil and a
pattern etching is carried out to obtain a desired printed
circuit.
During the activation treatment of the inside of holes and during
the pattern etching, the boundary layer i.e. the brass layer is
exposed to a solution containing hydrochloric acid. Further, after
the pattern etching, various plating processes may often be carried
out. In such case, the brass layer is exposed several times to
various plating solutions and acidic solutions. Since the brass
layer is hardly resistant to hydrochloric acid the brass layer is
corroded due to dezincification so that peel strength between the
copper foil and the base material is likely to be reduced.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a process for
surface-treating copper products, for example, a copper foil so as
to give a hydrochloric acid-resistant boundary layer between the
copper foil and a base material, in the preparation of a
copper-foil laminate.
The present inventors have made extensive research on such a
process and as a result have found that when a binary alloy of zinc
and nickel is used as a copper layer-coating metal on the surface
of the copper foil to convert into a ternary alloy of zinc, nickel
and copper at the time of laminating the copper foil on the base
material, the resistance to hydrochloric acid is improved, and also
have found a zinc-nickel composition which is readily convertible
into a ternary alloy of zinc-nickel-copper by a conventional
operation of preparing copper-clad laminates.
The present invention resides in a process for surface-treating a
copper product, which process comprises electrically depositing a
binary alloy consisting of 95 to 20% by weight of zinc and 5 to 80%
by weight of nickel, on the surface of a copper product to form a
coating layer, followed by laminating or heat-pressing copper
product thus obtained onto a base material so as to convert said
binary alloy into a ternary alloy of zinc, nickel and copper.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
As discribed above, in the preparation of copper-clad laminates, a
roughened surface of electrically deposited copper is formed on the
surface of copper foil to be bonded onto a base material to enhance
peel strength between the copper foil and the base material, and a
binary alloy is coated on the roughened surface of electrically
deposited copper. In order that the resulting coating layer does
not reduce the peel strength of said roughened surface, it is
preferred that the coating layer is as thin as to keep the
roughness, but on the other hand, the coating layer is necessary to
have a thickness enough to prevent granular copper from migration.
The thickness of such a coating layer has been usually about 0.08
.mu.m, whereas in the present invention, 0.002 .mu.m may be
sufficient since the ternary alloy of zinc, nickel and copper of
the present invention is superior in the capability of preventing
the migration and the resistance to acids. The coating layer is
faced to the base material and bonded thereto by heat-pressing. At
that time, a mutual diffusion occurs between the coating layer and
copper substrate, and conversion into a ternary alloy of
zinc-nickel-copper proceeds to give a boundary layer consisting of
the ternary alloy having a superior resistance to hydrochloric
acid. The operation of laminating the copper foil is carried out
usually at a temperature of about 170.degree. C. and a pressure of
about 20 kg/cm for one hour. In this case, if the nickel content in
the coating layer exceeds 80% by weight, the conversion into the
ternary alloy does not sufficiently proceed, while if the content
is lower than 5% by weight, the resistance to hydrochloric acid of
the ternary alloy lowers; hence the nickel content in the coating
layer is preferred to be 5 to 80% by weight. The nickel content is
more preferably 10 to 50% by weight. In this case, in the above
operation of lamination, the conversion into the ternary alloy
sufficiently proceeds as far as the surface of the coating layer
i.e. the boundary layer to the base material, and the boundary
layer exhibits a red-yellow color. Further the thickness of the
coating layer is preferably 0.001 to 0.15 .mu.m, more preferably
0.001 to 0.01 .mu.m. If the thickness exceeds 0.15 .mu.m, the
conversion into the ternary alloy does not sufficiently proceed in
a conventional operation of lamination, while if it is less than
0.001 .mu.m, the copper content in the ternary alloy becomes very
high during lamination unable to fully function as the ternary
alloy. In the case of a thickness of 0.001 to 0.1 .mu.m, the bond
strength and the resistance to acids are particularly superior.
When the surface treatment as described above, of the present
invention is carried out, the electrolyte used therein has the
following fundamental composition:
Potassium Pyrophosphate: 100 g/l
Zinc Pyrophosphate: 20 g/l
Nickel Pyrophosphate: 7.5 g/l
This composition corresponds to the case where the nickel content
in the binary alloy is 30% by weight. When the nickel concentration
of nickel pyrophosphate is varied, it is possible to vary the
nickel content in the binary alloy to be electrically deposited.
For example, when the concentration of nickel pyrophosphate is 1.2,
2.4, 14 or 19 g/l, the nickel content in the binary alloy to be
electrically deposited is 5, 10, 60 or 80% by weight. For example,
keeping the electrolyte at a pH of 9.5 and at a bath temperature of
25.degree. C., electro-deposition is carried out with a current
density of 0.2 A/dm.sup.2 for about 10 seconds.
The present invention will be described in more detail by way of
Example.
The process for surface treatment of the present invention can be
carried out generally in the acid-resistant treatment of the
surface of copper products besides a copper foil used for
preparation of copper-clad laminate. In these cases, copper
products do not always bond to base materials.
EXAMPLE
A roughened surface of copper electrically deposited on a copper
foil was coated by a coating layer of 0.005 .mu.m thick consisting
of a binary alloy of zinc and nickel having various nickel contents
indicated in Table 1. The resulting layer was bonded onto a glass
fiber-reinforced epoxy sheet at a temperature of 160.degree. C. and
a pressure of 20 kg/cm.sup.2 for one hour to form a copper-clad
laminate. In the case of a nickel content of 80%, the color of the
resulting boundary surface remained white-gray, while in the case
of 5 to 70%, the color turned into a red-yellow color.
For comparison, a conventional copper foil having zinc electrically
deposited thereon using a zinc-plating bath and that having
zinc-copper alloy electrically deposited thereon using a
conventional cyanide bath were prepared and copper-clad lamintes
were similarly formed from these copper foils. In addition, the
zinc-coating layer and the zinc-copper alloy-coating layer bath had
a thickness of about 0.005 .mu.m.
Next, copper-clad laminates wherein copper foils of the present
invention coated by the above binary alloys were used and the
copper-clad laminate wherein a conventional copper foil was used,
were compared by their immersion tests in an aqueous solution of
hydrochloric acid to determine the percentage deterioration of the
bond strength.
In addition, a rectangular pattern of 0.8 mm wide and 50 mm long
was formed on the respective copper-clad laminates according to a
conventional etching process to obtain testing samples.
The percentage deterioration was calculated from the following
equation:
wherein A: bond strength (kg/cm) after laminating of copper foil,
B: bond strength (kg/cm) after immersion in a 20% aqueous solution
of hydrochloric acid at 25.degree. C. for 30 minutes, each being
measured by 90.degree. peeling test, and C: percentage
deterioration (%) expressing the reduction extent from A into B.
The results are shown in Table 1. As apparent from this Table, the
percentage deterioration in the case where the copper foil of the
present invention was used is extremely low. This indicates that
the resistance to hydrochloric acid, of the boundary layer between
the copper foil and the base material is very high.
TABLE 1 ______________________________________ Ni-content A B C (%)
(kg/cm) (kg/cm) (%) ______________________________________ Present
1 2.20 1.54 30 Invention 5 2.20 1.98 10 10 2.25 2.18 3 30 2.25 2.22
1 50 2.25 2.2O 2 80 2.05 2.03 1 Zn layer 2.05 1.56 24 Zn--Cu 2.05
1.56 24 layer ______________________________________ Note: Zn
layer" and "Zn--Cu layer" refer to conventional products.
As apparent from the foregoing, the boundary layer of the copper
foil subjected to the surface treatment of the present invention
has a superior resistance to acids; hence in the process of
preparing printed circuits, there is almost no fear that the
boundary layer is corroded by an etching solution, an aqueous
solution of hydrochloric acid, etc. to deteriorate its bond
strength. Further, neither spotting nor staining occurs. Still
further, it has become possible to attain the above object by means
of a coating layer having a very small thickness which has never
been known.
* * * * *